In a typical disc drive, numerous components work together to read and write data from and to discs in the drive. The components typically have interdependent settings or specifications selected to achieve a desired level of performance. For example, filters in the servo system of a disc drive typically have cutoff frequencies to filter out unwanted frequencies, such as aliases. Component settings are typically set when the disc drive is designed and/or manufactured, but are usually not changed subsequently. Additionally, component settings are typically selected independently of each other, without consideration of interdependence among components within the disc drive.
One problem with current approaches to disc drive design and manufacture relates to changes in disc drive environment after the disc drive is designed or manufactured. Typically, after the disc drive is put into use, component settings are not changed. The manufacturers assume a type of environment and select component settings that are believed to yield optimal performance for the assumed environment. In actuality, the assumed environment often differs substantially from the actual operating environment. For example, the disc drive may be used at a significantly different altitude than was assumed, or at a different temperature, or be exposed to different vibrations than assumed. To the extent that the actual environment differs from the assumed environment, the selected component parameters will not yield optimal disc drive performance.
Another problem with current approaches to disc drive design relates to interdependence among components in the disc drive. As discussed earlier, selection of one component parameter often affects behavior related to another component parameter. It is the combination of parameters that dictate the level of performance of a disc drive. However, parameters are often selected independently of other parameters during design and manufacture, without consideration of how their selection will impact behaviors of other components, and hence, the overall performance of the disc drive.
A particular example that illustrates common performance problems relates to areal density and fly height control. Disc drives usually have a transducer that flies over the surface of a disc, reading and/or writing date from and to the disc. Areal density refers to an amount of data per unit area on the disc surface. Fly height refers to the distance the transducer is from the surface of the disc. Generally, as fly height decreases (i.e., transducer closer to the surface), areal density increases because when the transducer is closer to the disc surface, data reading and writing is generally more accurate and data can be spaced more closely.
Based on required areal density, a transducer fly height is targeted, and an air bearing is designed that will allow the transducer to fly at the specified height. If this is done correctly, then the areal density requirement is met. However great attention must be paid to the variability imparted during the manufacturing process. Parts that fly too low will be at risk for contacting the disc and thereby possibly causing a failing drive. Parts that fly too high will not allow the drive to meet the areal density requirement. A fly height is typically targeted once when the disc drive is manufactured to correspond to a targeted reliability and areal density. However, after the disc drive is delivered to a user, conditions, such as altitude, may change such that the previously targeted reliability and areal density are no longer met.
Accordingly there is a need for a system and method for improving disc drive performance with consideration to component interdependence and component variation over the life of the disc drive.